Integrated access and backhaul mobility

ABSTRACT

The present invention provides a mobile communication system sub-network comprising a macrocell base station, and a plurality of small cell base stations, the plurality of small cell base stations being in wireless communication with the macrocell base station, wherein each small cell base station is either in direct connection with the macrocell base station or is in connection with the macrocell base station via one or more other small cell base stations, wherein the macrocell base station is arranged to configure a UE device having a RRC connection to the macrocell base station with candidate small cell base station information for enabling the UE device to switch autonomously between small cell base stations, and wherein the macrocell base station is arranged to configure the small cell base stations with small cell base station configuration information.

The present invention relates to a method of operating a mobilecommunication network in which user equipment, UE, devices can switchbetween communication cells.

Known cellular mobile communication networks comprise a core network(CN) and one or more radio access networks (RANs). The CN comprisesamongst others functions for authentication and authorization of usersand devices, for quality of service (QoS) management and control, forproviding access to various data networks and for data routing betweenthe RANs and data networks. The CN is typically radio access technology(RAT) agnostic, i.e. it comprises only functions that do not relate to aspecific RAT or RAN.

Each RAN comprises functions that provide to user equipment (UE) deviceswireless radio access to the core network. Some of these functions arespecific for the used RAT, e.g. UMTS, LTE or 5G new radio (NR). A RANconsists of multiple macro base stations of a specific RAT (NB, eNB,gNB) and it may additionally comprise a number of small cell basestations (SCs) of the same or a different RAT.

UE devices that are registered in the CN may have a current connectionto a RAN and the CN, i.e. they are in connected mode, or they do nothave such a connection, i.e. they are in idle or inactive mode. For UEdevices in connected mode, there is typically one base stationcontrolling the device, called serving base station or serving cellthroughout this document. This serving base station is using the radioresource control (RRC) protocol to establish an RRC context in both, theUE and the base station. The RRC context comprises the UE device's radiocapabilities, the current setup of bearers with respective QoS, themultiplexing of services or applications on these bearers and themultiplexing of these bearers onto physical resources, the allocatedusable resources and measurements to be performed by the UE device andtriggers and content for the reporting of such measurements. Themeasurement configuration comprises neighbour cells to be measured,which neighbour cells may operate on the same RAT and same frequency asthe controlling base station, same RAT and different frequency ordifferent RATs.

When measurement reports received in the serving base station indicateneighbour cells to be more appropriate for communication than theserving cell, the base station may execute a handover procedure in whichit prepares a selected target cell for the handover and commands the UEto handover to the target cell. During preparation, the target cellreceives the RRC context from the serving cell so that the communicationbetween UE and target cell can continue basically from the state it hadin the serving cell.

US 2011/0143738 A1 describes autonomous search functions (ASFs) that arefunctions that modify their own functionality in response to externalinputs, optimizing search strategy to the environment. Mobile devicesuse ASFs on an LTE network to scan a range of frequencies to findinformation broadcast by cells. Information broadcast by UTRA and E-UTRAcells may include the cell's closed subscriber group (CSG) ID,information specifying supported protocols, information specifyingsupported radio access technology (RAT), and the rating of the cellwithin its frequency, as well as other information identifying the celland how to connect to it. The mobile device may use information aboutdetected cells to initiate proximity detection messages for callhandover or handover avoidance. When a mobile device enters or leavesthe proximity of another cell while connected to a UTRA or E-UTRA basestation, the network may initiate handover messages between the mobiledevice's current base station and the detected cell's base station.

U.S. Pat. No. 9,717,110 provides methods for wireless communicationbetween a first and second wireless communication devices, the firstdevice sending a chirp signal to the second devices in a mesh networkduring a first wake-up period common to the first and second devices.The first device further receives a keep alive signal and connectionsetup information from a determined wireless relay device from among thesecond devices during the first wake-up period, the connection setupinformation comprising resource allocation information. Further adownlink page may be transmitted to the first device together with theconnection setup information.

US 2017/0055192 A1 describes a UE centric mobility mechanism in which aUE performs cell-reselection during RRC connected mode, when extendedDRX is used, i.e. when the UE does not receive data for a longer periodof time. The reselection criteria are received from a source cell in RRCconnected mode and the UE decides about whether network-controlledmobility or UE autonomous cell re-selection is applied based onconditions, e.g. whether extended DRX is used. When using UE autonomousre-selection and signaling is required in a target cell, a RRCreestablishment procedure is used by the UE to establish a connection tothe target cell. As a result the target cell fetches the UE context fromthe source cell, similar to an RRC connection establishment orresumption from idle mode.

EP 2 879 440 A1 describes a technique for controlling a small cell basestation in a system comprising small cell base stations controlled by amacrocell base station. The small cells take measurements andinformation is reported to the macrocell base station.

WO 2017/028808 A1 discusses a method of connected mode cell reselectionin which a UE can perform cell reselection without handover signaling.EP 3 125 640 A1 describes a bearer management procedure where the UE hasdual connectivity, changing a bearer type between a master cell groupand a secondary cell group. WO 2015/065010 A1 describes a method forperforming dual connectivity in a heterogeneous network comprising forexample a macrocell base station and small cell base stations.

Wireless relays are known from LTE. They are base stations that connectwirelessly via so called donor base stations (DeNB) to the core network.Towards the UE devices served by the wireless relay, the relay lookslike a normal base station that controls the UE device, i.e. an RRCconnection is setup between the relay and the UE device. The wirelessrelay acts similar to a UE towards the DeNB, but the radio resourcesused between UE and relay are controlled by the DeNB or by the CN to acertain extent.

Dual or multi connectivity mechanisms are known from LTE and NR in whicha single UE device has an RRC connection and an active radio connectionto a serving cell, in that case called primary cell, and in addition ithas one or more active radio connection to secondary cells. The primarycell controls the UE device and it also controls the secondary cellswith regard to the UE device. The base station providing the secondarycell for a UE device may in parallel control other UE devices as aprimary or serving cell. The addition and removal of secondary cells tothe UE is completely under control of the primary cell.

For the migration of an LTE network towards new 5G NR techniques, dualconnectivity is introduced with a UE device having a primary cellproviding an LTE connection and secondary cells providing 5G NRconnections, or vice-versa. In that case also the secondary cells havean RRC connection with the UE device of the respective secondary RAT,but the primary cell is still in control of the connections includingaddition and removal of secondary cells.

For a single UE device, the serving base station is typically the onlyor the main access point to the core network. That is, the exchange ofcontrol messages with the core network, so called NAS signaling, isrouted through this base station to the core network. Also, the userdata is routed via the serving cell, except for some dual connectivityscenarios in which multiple CN access points are used for user datarouting. In case the CN needs to initiate signaling or data transfertowards the UE, it requests signaling or data transfer at the servingbase station.

3GPP recently started studies of the usage of the 5G NR RAT for wirelessbackhaul links, typically used for small cells (SCs). The aim of thestudy is to allow a low cost and low effort SC deployment by connectingthe SCs wirelessly to a controlling base station, so called donor nextgeneration Node B, DgNB. The study includes multi-hop scenarios thatconnect a SC wirelessly to another SC until a final SC in the pathoffers a direct link to the DgNB.

A new multi-hop wireless RAN may use different architecture alternativeswith respect to which node, i.e. which base station, has control of themulti-hop RAN and the UE devices connected to that RAN. Each solutionhas its benefits and drawbacks.

Similar to the known wireless relays of LTE, each base station (SC) inthe multi-hop RAN may act as a full base station towards a served UEdevice or towards a served SC. For its backhaul link such a SC wouldthen act similar to a UE device served by the next hop SC or the DgNBfor the topmost SC layer. Drawbacks of this solution are that eachhandover of UEs between SCs would require a context transfer between SCsover the hierarchical multi-hop RAN. As security keys for encryption andintegrity protection are setup between the serving base station and theUE device, the SCs would need to be built accordingly, i.e. located at anon-accessible place or secured with a housing that secures the securitykeys from being read out. This would increase the price for such SCsignificantly. Also, no single node has control of the multi-hopnetwork, thus each SC would need knowledge about surrounding neighbourcells to properly configure measurements in the served UE devices. Thiswould make an easy setup of such wireless SCs difficult and may requireintervention of an operation and maintenance system necessary for eachnewly setup SC. Another drawback is that each SC in that architecturewould be the serving RAN node of a UE for the CN, i.e. every handover ofa UE between SCs would require an update of the respective CN node.

An alternative approach is the termination of each RRC connection in theDgNB, i.e. all UE devices as well as the SCs with a wireless backhaulvia the multi-hop RAN would setup an RRC Connection with the DgNB, whichin turn controls all devices within the multi-hop RAN. This would allowan easy setup of SCs, which are fully configured by the DgNB. Assecurity in that case is setup between each device and the DgNB,security of served devices would not be an issue in any of the SCs andthus the price of the SC and its placement can be reduced.

However, the latter architecture alternative introduces latency to theconnection between devices and their serving base station, now being theDgNB, which contradicts the requirement of some functions in a servingbase station to be performed very quickly and resulting configurationsreaching the served devices quickly. One example of such low delayprocedures is the measurement reporting and resulting handoverdecisions.

The present invention overcomes the drawback of the DgNB-centricmulti-hop RAN and makes that architecture the most beneficial solutionfor SC deployment.

The present invention provides a mobile communication system sub-networkcomprising a first, or macrocell, base station and a plurality ofsecond, or small cell, base stations, the plurality of second basestations being in wireless communication with the first base station,wherein each second base station is either in direct connection with thefirst base station or is in connection with the first base station viaone or more other second base stations, wherein the first base stationis arranged to configure a user equipment, UE, device having a radioresource control, RRC, connection to the first base station withcandidate second base station information for enabling the UE device toswitch autonomously between second base stations, and wherein the firstbase station is arranged to configure the second base stations withsecond base station configuration information, the second base stationconfiguration information enabling the second base stations to transmitdata to and receive data from the UE device and to multiplex and routedata from and to the UE device.

The invention further provides a corresponding UE device, small cellbase station and method of operating a mobile communications network.

Preferred embodiments of the invention will now be described, by way ofexample only, with reference to the accompanying drawings in which:

FIG. 1 shows a schematic arrangement of a multi-hop wireless backhaulnetwork;

FIGS. 2 a, 2 b and 2 c show protocol stack layers;

FIG. 3 is a schematic illustration of a sub-network;

FIG. 4 is a message sequence chart

FIG. 5 is a further message sequence chart;

FIG. 6 is a schematic illustration of a further sub-network arrangement;

FIG. 7 is a message sequence chart;

FIG. 8 is a schematic illustration of a further sub-network arrangement;and

FIG. 9 is a message sequence chart for the sub-network of FIG. 8 .

FIG. 1 shows an example multi-hop wireless backhaul RAN with a 5G newradio (NR) donor base station (DgNB) connected to a CN. The DgNBcontrols a subnetwork of multiple cascaded small cell base stationsconnected wirelessly. Each small cell base station has one wirelessbackhaul link to another small cell base station or to the DgNB and zeroor more access links to other small cell base stations or to UE devices.

The DgNB has access links 1 and 5 to small cells SC2.1 and SC2.2,respectively.

The small cell base station SC2.1 has access links 2 and 4 to smallcells SC3.1 and SC3.2, respectively. In addition, SC2.1 provides anaccess link to UE device UE3. The small cell SC2.2 has access links tosmall cell SC3.3 and to UE device UE5.

The small cell SC3.1 provides NR connectivity to two UE devices UE1 andUE2 and small cell SC3.2 provides NR connectivity to UE device UE4 viarespective access links.

According to the present invention, all small cells and UE devices inthe given example have an active connection to the RAN and via the RANto the CN which may further provide connections to various data networks(not shown). UE devices UE1, UE2 and UE4 have established an RRCConnection to the DgNB via a first link, e.g. link 3, to a first smallcell which is connected via a wireless backhaul link, e.g. link 2, to asecond small cell. The second small cell is connected wirelessly, e.g.via link 1, to the DgNB. UE devices UE3 and UE5 have as well an RRCconnection to the DgNB via a direct connection to small cells that arewirelessly connected to the DgNB.

All radio links in UL and DL have an inherent identification of thetransmitting devices, i.e. a receiving base station in all legacycellular radio communication systems can distinguish data received fromdifferent transmitting devices and the devices know from which basestation they receive.

According to the current invention, all small cells of the example havean RRC connection to the DgNB, either via a direct wireless backhaullink or via a wireless backhaul to another small cell.

Small cell base stations in this new architecture are similar to layer 2relays. They do not control the access of UE devices to the RAN orconfigure the device, both is done by the DgNB. They provide radioresources over an access link to served UE devices and to served smallcells according to their configuration received from the DgNB. Indownlink, they decode data received on the wireless backhaul link andreassemble segmented data packets and further they segment and encodethe packets for forwarding on a wireless access link to the next smallcell base station or to the UE device. In uplink, the small cell basestations decode data received on the access link and reassemblesegmented data packets and further they segment and encode the packetsfor forwarding on a wireless backhaul link to the next small cell basestation or to the DgNB.

In order to allow QoS to be provided throughout the described multi-hopnetwork, different bearers from different UE devices need to bedistinguished within every small cell. Only then the small cells canapply a bearer and UE device specific priority and resource allocation.As a result, on the air interfaces between two small cells or between asmall cell and the DgNB an indication of the originating UE device andbearer is required for every data packet. That is, small cells need tobe able to distinguish data packets from one bearer of a UE from anotherbearer of the same UE. As well, they need to be able to distinguish datapackets from one bearer of a UE from a bearer of another UE.

The air interface, e.g. on a wireless backhaul link, provides inherentlythe information who is the originating device that transmitted the datain the UL, i.e. who is the peer device of a single hop. Also, the airinterface provides a bearer identification for that hop, but on eachfurther hop, the originating device as well as bearer information islost.

According to this invention, a small cell multiplexes all data receivedfrom bearers of the previous hop that have similar or the same QoS,potentially from different originating devices, onto one bearer of thenext hop with respective QoS. The so multiplexed data is transmittedover the air interface between two small cells. An indication of theoriginating bearer and device is injected or added to the data packets.This indication is used at the receiver to again decide aboutmultiplexing of the data onto the next hop bearers. This enables eachsmall cell base station to forward packets according to their individualQoS and priority.

Bearers are indicated on the legacy air interface, e.g. LTE, byindicating the logical channel identification (LogCh-ID) in the MACheader of a data packet. The LogCh-ID is, however, only unique within asingle RRC Connection between a UE device and a serving base station.Other devices may use the same LogCh-ID to indicate their bearers. Basestations use the inherent UE device identification on the physical layerto uniquely identify the packet originator.

In this invention, for treatment of packets in a cascaded small cellbase station network, an identification is required that combines the UEdevice identification and the bearer. The bearer in this sense is a termused for any data flows that have a common or similar QoS and priority.In legacy radio access networks this is usually termed bearer. The restof this invention will use that term without losing generality. Similarto the (LogCh-ID), we call the indication of originating UEs and bearersjointly a global logical channel identity (GLogCh-ID) which is then usedwithin the multi-hop network on each hop.

The GLogCh-ID is unique for every bearer of every UE device servedwithin sub-network. The UE device may still be identifiable in theGLogCh-ID, e.g. if this identifier has two parts, a UE device identityunique for the UE device in the subnetwork and a LogCh-ID unique for abearer of a single UE device, similar to the LogCh-ID used in today'sprotocol stack. Alternatively, the GLogCh-ID does not have separateidentifiers for UE and bearer.

The DgNB is in control of the multiplexing. It configures all smallcells with the GLogCh-ID and respective QoS and priorities of thedevices for which they are configured to actually or potentially serveas a router or for providing an access link.

To simplify the description, in the following we focus our descriptionon only a few nodes of those shown in FIG. 1 : UE1, SC3.1, SC2.1, links3, 2 and 1 and the DgNB.

FIGS. 2 a, 2 b and 2 c show the protocol stack layers as advantageouslyused in the involved nodes based on the currently envisaged protocolstack layers of the NR air interface.

FIG. 2 a shows the protocol stack for the establishment and maintenanceof the RRC connection between UE device UE1 and the DgNB (Control Plane)via small cells SC3.1 and SC2.1. An RRC connection is establishedbetween UE UE1 and the DgNB, so that the RRC protocol peers reside inthe UE device and the DgNB. A security association is established aswell between these two entities and the PDCP protocol layer is using thesecurity association, i.e. the respective shared keys, to encrypt andintegrity protect the RRC messages. The protocol layers below PDCP, i.e.radio link control protocol (RLC), medium access control (MAC) and thephysical layer (PHY) are related to an actual radio link. They aretherefore present in each involved node and each hop is established bythe respective peer protocols on either side of the hop.

For each hop between network nodes, i.e. between two small cells orbetween a small cell and the DgNB, a function is required to multiplexthe received packets onto the next hop bearers and to indicate theGLogCh-ID newly introduced in this invention. For this, the protocolstack of each of these hops comprises in addition to the known functionsof RLC, MAC and the physical layer a relaying function that carries in aheader field of transmitted packets the GLogCh-ID and that decides,based on the configuration by the DgNB, on the next hop bearers ontowhich to multiplex the packets. This relaying function could beperformed in the RLC layer as an additional function with an additionalRLC header field. Alternatively, the hop-to-hop protocol stack couldinclude an additional and enhanced PDCP layer for that function. FIG. 2a shows another alternative for the function in an additional protocollayer named Relaying Protocol (RP) without loss of generality.

Similarly, FIG. 2 b shows the respective protocol stack for the transferof user data from the UE device UE1 to the DgNB. The protocol formultiplexing of service data flows on data radio bearers (SDAP) newlyintroduced for 5G NR and the PDCP protocol for encryption, integrityprotection and control data compression are present in UE1 and the DgNB.Again, the protocol layers below PDCP, i.e. radio link protocol (RLC),medium access control (MAC) and the physical layer (PHY) are related toan actual radio link and are therefore present in each involved node.The newly introduced relaying function with indication of the GLogCh-IDand multiplexing is again shown as the relaying protocol (RP) whilealternatives exist as described above.

FIG. 2 c depicts the protocol stack for the establishment andmaintenance of the RRC connection between the small cell SC3.1 and theDgNB. RRC and PDCP peers are in SC3.1 and DgNB respectively, RLC, MACand PHY are hop-by-hop. The relaying function, e.g. in the RP-layer, isonly required in the second hop of that connection, i.e. SC2.1 to DgNB.A protocol stack for establishment and maintenance of an RRC connectionbetween SC2.1 and DgNB, which is not shown in any figure, would lookvery similar to FIG. 2 c , yet with a direct peer of every protocolstack layer between SC2.1 and DgNB.

Based on the architecture described above, one aspect of this inventionis the configuration of candidate handover target small cells by theDgNB. The configuration is performed so that a UE device is enabled toautonomously switch the connection from a current source small cell toone of the candidate target small cells, based on criteria configured bythe DgNB, but without reporting measurements related to the source andtarget cell and without being ordered by a base station to perform ahandover.

The UE device is configured with a set of candidate small cells, i.e.cell identities, frequency resources and radio parameters. Theconfiguration may comprise further information like the mode ofaccessing the target cell, e.g. via RACH or via direct resource requeston an uplink control channel. Also, the configuration comprises criteriato switch cell, e.g. a threshold below which the current source cell hasto fall before cell switching is considered, thresholds for comparingthe source and target cells, a duration for which a target cell musthave a reception signal strength with a threshold above the source cellor other criteria. In the event the criteria are met, the UE immediatelyswitches to the target cell.

Above candidate list of potential target cells is very different fromthe well-known neighbour cell list, which comprises cells to measure andreport to the serving cell under certain criteria so that the servingcell can decide to prepare handover and order the UE device to perform ahandover. The legacy neighbour cell list configuration and relatedmeasurement and report configuration and performance can thus continuein parallel to this invention for potential target cells that are notunder the control of the DgNB serving the UE device.

Also, the candidate list and autonomous cell switch is very differentfrom a cell selection after radio link failure in a serving cell, asthis requires the UE to go through Idle state, i.e. setup a new RRCcontext with the selected cell.

The configuration of candidate small cells is not only done in the UEdevice. The DgNB configures the candidate target small cells as well toenable data transfer via a target cell to immediately start after a cellswitch.

The DgNB configures candidate target cells with all information requiredto transmit and receive data and to multiplex and route data (controland user data) from and to the UE device. That is, the candidate smallcells are configured with

-   -   MAC layer configuration comprising        -   Information about existing signaling and data bearers            established in the UE device,        -   Multiplexing information for multiplexing the bearers onto            transport channels or physical resources,        -   Priority information, e.g. priority of bearers of the same            UE relative to each other, and/or priority of the UE device            relative to other UE devices or small cells served by the            same small cell,    -   Physical layer configuration comprising        -   A UE device identity (UE-Id), e.g. a C-RNTI as known from            LTE, with which the UE can identify itself when accessing a            target cell        -   Radio capabilities of the UE device and radio parameters    -   One or more Global Logical Channel Identities (GLogCh-IDs) that        are to be transmitted together with data received from the UE        device to allow proper multiplexing in further hops.    -   Routing information for transport of UL and/or DL information        from or to the UE device.

The DgNB configures the above information into candidate small cells,i.e. small cells that a UE device may directly access via a radio linkconnection. In addition, the DgNB configures all small cells that are onthe route between any of the candidate target small cells and the DgNB.These routing small cells that do not provide an air interface to the UEdevice, are configured with

-   -   GLogCh-IDs that are used to identify data of different QoS        and/or priority (i.e. of different bearers) originating from or        addressed to the UE device,    -   Associated QoS and/or priority information, and    -   Routing information for transport of UL and/DL information from        or to the UE device.

To summarize, all small cells potentially involved in routing of datafrom a UE device are configured with information required to forwarddata packets from or to the UE device according to the packet'sindividual QoS requirements. Small cells that are candidates to servethe UE device's radio link in addition, are configured in addition witha UE device identity and physical and MAC layer parameters for setup andmaintenance of the radio link.

A UE switching to a target cell requests UL resources from the targetcell with its UE-Id. The target cell can identify the UE based on thepre-configured UE-Id and provide available resources according to thebearer, multiplexing and priority information. The resources arerequested by the UE for transmission or user data or control data, e.g.application data or RRC messages, which also serves as an indication forthe target small cell base station that the UE has switched cell.

The UE device will ideally reset its RLC and MAC entity so that nofurther context transfer from the source small cell is required.Depending on the required QoS of the bearers, lost packets can beretransmitted on PDCP layer between UE device and DgNB. As the UE devicehas a security association with the DgNB, all data is encrypted andoptionally integrity protected so that the target small cell does notneed to perform any security setup procedures with the UE device.

In order to ensure a quick route switch within the subnetwork and routeDL traffic towards the new small cell, as soon as the UE device arrivesin a small cell, the small cell will inform the next higher small cellabout the UE now being served by that target small cell. This isrepeated by all small cells up the hierarchy until a base station isreached that is part of the old as well as the new route. We may callthis base station the joint base station, which is either a small cellor the DgNB. The joint base station will immediately start routing DLpackets along the new route to the target small cell. The trigger for asmall cell to inform the next hop small cell about a UE device arrivalmay be the UE providing its UE-ID in a resource request. The preferredalternative is that a first data packet, e.g. comprising an RRC messagefrom the UE to the DgNB, arrives at the small cell. This packet, routedalong the new path, indicates the path switch to be established to anysmall cell on its way up to the joint base station. That is, the firstUL packet serves as the indication of the UE arrival for further smallcells. Alternatives are that the small cells have a peer-to-peersignaling, i.e. via their backhaul MAC layer or via a new SC-to-SCprotocol.

As described, one beneficial aspect of the new DgNB-centric architectureis that security takes place between UE device and DgNB so that the UEand small cells do not have to perform additional security proceduresthat would delay the cell switch. One drawback of the non-existence ofsecurity associations between the UE device and any small cell is thepossibility of security attacks from fraud UE devices simply accessing asmall cell with a fake UE-Id or with a real UE-Id from a fraud device,injecting false data in UL and routing UE device related data towards anew small cell and potentially away from an actual small cell servingthe respective UE device.

Using integrity protection will prevent data from a fraud UE device tocause any erroneous data to be successfully injected in a data stream.Also, encryption will ensure data cannot be read by the fraud UE device.However, denial-of-service attacks may still be an issue because there-routing to the new target cell initiated by a fraud UE device willprevent data from reaching the correct target UE device.

In order to prevent this kind of attacks, the joint base station willtemporarily duplicate packets in DL to both, the new and the old route.Also, it will accept UL packets from both routes to be forwarded alongthe single route above the joint base station. Any duplicated packetswill be filtered in the DgNB using PDCP sequence numbers or integrityprotection means.

Finally, the UE device itself will inform the DgNB about its switch ofthe serving cell in an RRC message which will be generated by the UEdevice, obviously with security, and when received, the DgNB is informedabout the cell switch. The impacted small cells may in addition informthe DgNB via their RRC or a similar protocol about the changes that haveoccurred. The DgNB in return informs the impacted small cells about theswitch of the route, i.e. small cells below the joint base station onthe old path may be informed to stop routing to and from the UE, thejoint base station is informed to stop duplicating packets and use thenew path only and UE as well as small cells are informed about newcandidate small cells for a potential future autonomous handover.

The joint base station may apply packet duplication only for limitedtime. It may start a timer which is stopped when a new route isconfirmed by the DgNB. If the time expires before a confirmation isreceived, the DgNB may stop packet duplication and return to the oldroute assuming that the new route is not appropriate.

Because of the inventive autonomous cell switch described herein, thedata transfer been UE and the core network is continued during the timethe DgNB is not informed about the cell switch or has not informed thesmall cells appropriately, and data delay is kept at a minimum. Thisinvention thus overcomes the latency introduced by multi-hop radiosub-networks.

In DL, the new route will only be used after the joint base station hasgot the information about the path switch. Between the switch by the UEdevice and first DL packets routed to the target small cell, somepackets may be delivered in DL along the old route. To reduce thelikelihood or the number of lost packets, the UE device, depending onits capabilities, may continue to receive packets from the source smallcell until a first packet has arrived in DL in the target small cell. Areset of the RLC, MAC and PHY layer in the UE will then only take placewhen a first DL packet in the new cell arrives.

If the UE device uses a communication service that requires veryreliable data transfer, redundant transmission of data may be beneficialto overcome packet losses. The newly introduced architecture of thisinvention may be advantageously used also for this case. A UE may havemultiple serving small cells and a configuration of candidate targetsmall cells for autonomous mobility. The UE may now use the mechanismsdescribed to switch one of the small cells autonomously while keepingother redundant links unchanged. Only when UL and DL transmission viathe autonomously selected target small cell is confirmed, e.g. by afirst DL packet arriving or by a respective DL RRC message received fromthe DgNB, the redundant other links can be switched. The redundanttransmission can be a bearer QoS setting used permanently for a specificbearer or it is a feature used temporarily only in conjunction with thedescribed small cell switch to prevent packet loss.

The current invention can also be used for dual connectivity where asingle UE device is connected in parallel to different base stations.The UE device may be connected to two or more small cells controlled bythe same DgNB and use the autonomous switching techniques to select thebest cells. The UE device may alternatively be connected to a first basestation and a small cell controlled according to this invention by aDgNB, the first base station not being controlled by the DgNB. Then theautonomous switching techniques are used to select the best small cellwhile the first base station stays the same or is changed by legacyhandover procedures.

Yet another alternative to the architecture of FIG. 1 is a UE that hastwo or more parallel connections to the same DgNB, one via a direct airinterface and one to a small cell with wireless backhaul as describedherein. The control signaling may then go via the direct link to theDgNB while the UE is configured to autonomously select the best smallcell for the parallel connection. The main reason for the autonomouscell switch, overcoming the control signaling delay of measurementreporting and handover performance introduced by the multi-hoparchitecture of cascaded small cells, however, is not present in thisuse case.

Yet another use case for the current invention is the use of multiplesmall cells for a single UE device for multiple bearers so that anoptimal small cell is selected by the UE device for different radiobearers. It may be that some small cells are optimized for some featureswhile they provide other features only limited or not at all. An examplecould be small cells that are specialized for low latency applications,but that cannot offer high data rate. These small cells could broadcasttheir nature to allow UE devices to take the information into accountwhen selecting new small cells, or the candidate cell configuration fromthe DgNB comprises special features of the small cells. The autonomouscell switch described in this invention would then be performed by theUE device for only a part of the bearers, the UE has setup or willsetup. The mechanisms apply as described and the GLogCh-ID of UL packetswill enable the joint base station to apply DL route adaption only forrespective bearers. Also, the route confirmation received later from theDgNB will confirm a new route for some bearers of the UE device whileother bearers are still routed along an old route. This use case of thepresent invention is especially useful for new data traffic types “ultralow latency (ULL)”, “ultra reliability (URL)” and “massive internet ofthings (MIoT)” of the developed 5G network, that may be used for somebearers of a UE device, while other bearer may be used for usualbroadband traffic. An example deployment could provide a low latencysmall cell base station in coverage of a UE device directly connected tothe DgNB, bypassing multiple wireless backhaul hops of alternative smallcell base stations in UE device coverage. The low latency small cellbase station offering only limited bandwidth or only connection lessdata communication, while other small cell base stations offer differentservices over a more efficient but slower multi-hop wireless backhaul.

The mechanisms described above allow autonomous switching of the servingcell for UE devices. The new architecture as shown in FIG. 1 is based ona wireless backhaul for the involved small cell base stations. Thewireless backhaul between small cells is based on the same or a similarair interface as the air interface between a UE device and a small cell.The inventive mechanisms of the current invention can thus be appliedalso on the wireless backhaul itself.

A small cell base station, e.g. SC3.1, being served by another smallcell base station, SC2.1, may be configured with candidate small cells,e.g. SC2.2, for autonomous cell switching. The candidate small cell isprepared with routing and multiplexing information as well as radio andidentity information, so that small cell SC2.2 can take over servingSC3.1 after a cell switch. The mechanisms described above can all beused accordingly, e.g. route switching, packet duplication and finalroute manifestation by the DgNB via Layer 3 signaling. A GLogCh-ID wouldonly be configured for bearers originating from the small cell SC3.1itself, as bearers routed by SC3.1 originating from other devices, e.g.UE1 and UE2, are already associated with a GLogCh-ID. Assuming a smallcell does not generate any user data, only signaling radio bearers forsetup and maintenance of the RRC connection between SC3.1 and DgNB wouldbe identified with GLogCh-IDs and associated with QoS and/or priorityinformation in the candidate small cell SC2.2.

This application of the current invention to the wireless backhaulconnection allows a flexible dynamic backhaul setup. However, becausesmall cells are assumed not to be mobile, the number of candidate smallcells for automatic cell switch in this case is assumed to be much lowerthan that of (usually mobile) UE devices. The switching option may be acounter measure against dynamic shadowing effects between two smallcells or against outage of small cells. Mobile small cells, however, mayprofit from the described network architecture and mechanisms similar toUE devices.

The preparation of a candidate small cell to serve as wireless backhaulfor another small cell after autonomous cell switching requires that thecandidate small cell is informed about all current and potential futurebearers served or routed by the source small cell. That is, if awireless backhaul network is bigger and has a deeper hierarchy than theexample network of FIG. 1 and a small cell routing traffic of severaltens of other small cell each with a number of UE devices, theconfiguration information for preparation of each small cells forautonomous switching will grow large. The configuration and its updatewill consume a lot of bandwidth of the wireless network and computeresource in the DgNB and small cells.

An alternative may then be to have an identical full configuration ofall small cells of a wireless backhaul, i.e. every small cell isconfigured with the full information of served bearers and devices, e.g.all GLogCh-IDs and related priorities and QoS. The configurationinformation can then be broadcasted from the DgNB, i.e. a fullconfiguration is provided once by the DgNB to all small cells directlyconnected to the DgNB and the small cells after reception of theconfiguration information, store and apply the configuration and forwardthe information to all further small cells that are served with a directlink. The same mechanism could apply to configuration updates that onlycomprise changes of the full configuration stored. The broadcastmechanism would require a common security key for integrity protectionto be available in all involved small cells to ensure correctness of theconfiguration information. The security can be achieved either with asymmetric key provided via dedicated layer 3 signaling from the DgNB toeach small cell or with an asymmetric key pair of the DgNB the publickey of which is pre-configured or included in the broadcast as acertificate verifiable by the receiving small cells.

The described broadcast prepares every small cell as a candidate forcell switching of all devices, UEs and small cells. A candidateconfiguration in the switching devices with candidate small cells willensure that switching is still limited under DgNB control. Also, itwould be possible to use multicast, i.e. a broadcast of differentconfiguration messages addressed to a group of small cells. This wouldreduce the single configuration messages in bigger hop-to-hop wirelessbackhaul subnetworks.

It should be noted that the description of the current invention doesnot prevent the wireless backhaul connection of small cell base stationto be secured, e.g. with a secure tunnel like an IPSec tunnel, toprevent eavesdropping and data manipulation at that level. This optionis not further described in this invention as is does not impact theinventive steps and benefits of the current invention, it is simply animplementation option.

FIG. 3 shows a simplified architecture comprising a DgNB, three smallcell base stations SC2, SC3.1 and SC3.) and a UE device UE. The UEdevice has an access link to small cell base station SC3.1. The smallcells SC3.1 and SC3.2) have wireless backhaul links to small cell basestation SC2 which has a wireless backhaul link to DgNB. The DgNB isconnected to the core network of an operator network.

FIG. 4 shows in a message sequence chart a message and data exchangewithin the subnetwork depicted in FIG. 3 . As a prerequisite and shownas a single box without details it is assumed that according to the basearchitecture of this invention all small cell base stations and the UEdevice have an RRC connection with the DgNB.

In the initial state of FIG. 4 , the UE has ongoing uplink UL anddownlink DL data transfer. For that purpose, small cells SC3.1 and SC2are configured according to this invention so that they can provide QoSto the data bearers the UE has currently setup. The UE device has a UEdevice identity, e.g. a C-RNTI according to the LTE standard, allocatedwhich the UE device uses in UL transmissions to indicate the originatorof the data. This may be done by scrambling UL messages with the UEdevice identity or by transmitting the plain identity or parts thereofas part of the data. The UE device identity is also used by the servingsmall cell for DL data transmissions to address resources used totransmit the data to the UE device. Again, scrambling or othertechniques may be used to carry the UE device identity or parts thereofin the DL resource allocation. According to the present invention, smallcell base station SC3.1 is configured with the C-RNTI of the UE device.The UE device may in addition be provided small cell specific resourcesin time and/or frequency domain for requesting UL scheduling from thesmall cell base station SC3.1. Other radio parameters concerning theradio features supported or preferred by the UE device may also beconfigured similar to known radio standards as LTE or 5G NR.

The UE may have three signaling radio bearers and four data radiobearers, in sum seven radio bearers with relevant QoS parameters aslisten in Table 1. The respective information is configured in the UEdevice and in the small cell base station that currently serves the UEdevice SC3.1.

TABLE 1 Relative LogCh-ID RB-Type Priority GLogCh-ID 1 SRB0 1 65 2 SRB11 66 3 SRB2 4 67 4 DRB1 Best effort 6 68 5 DRB2 SIP Signaling 3 69 6DRB3 VolP 2 70 7 DRB4 Video Streaming 5 71

Small cell base station SC3.1 has a wireless backhaul link to small cellbase station SC2 which may have eight radio bearers configured, threesignaling radio bearers to setup and maintain its own RRC connection tothe DgNB and five data radio bearers for forwarding or relaying datawith different QoS. Table 2 shows in an exemplary manner the wirelessbackhaul bearers configured for SC3.1 in SC3.1 and SC2. Only the threesignaling radio bearers originating from SC3.1 are allocated a GlobalLogical Channel Identity as all forwarded or relayed data are expectedto already comprise a GLogCh-ID according to their originating deviceand bearer.

TABLE 2 Relative LogCh-ID RB-Type Priority GLogCh-ID 1 SRB0 1 101 2 SRB11 102 3 SRB2 4 103 4 DRB1 Best effort 6 — 5 DRB2 SIP Signaling 3 — 6DRB3 VolP 2 — 7 DRB4 Video Streaming 5 — 8 DRB5 Conversational 2 — Video

Similarly, for small cell SC3.2 information may be configured in SC3.2and SC2 according to Table 3:

TABLE 3 Relative LogCh-ID RB-Type Priority GLogCh-ID 1 SRB0 1 104 2 SRB11 105 3 SRB2 4 106 4 DRB1 Best effort 6 — 5 DRB2 SIP Signaling 3 — 6DRB3 VolP 2 — 7 DRB4 Video Streaming 5 — 8 DRB5 Conversational 2 — Video

Small cell base station SC2 is configured according to this inventionwith information of devices that are or may potentially be served bySC2, e.g. GLogCh-ID, QoS and priority information, the information maydiffer from that configured in the served devices. For example, priorityinformation in small cell base station SC2 may take into account thathigh priority signaling radio bearers of the small cell base station SC2itself have a higher priority than similar bearers forwarded or relayedby SC2. Also, high priority signaling radio bearers of small cell basestations served by SC2, e.g. SC3.1 and SC3.2, may have higher prioritythan signaling radio bearers of UE devices. Thus, an example of datarelating to the UE device UE and small cell base stations SC3.1 andSC3.2 configured by the DgNB into SC2 is shown in Table 4. In addition,small cell base station SC2 is configured with its own signaling anddata radio bearers similar to base stations SC3.1 and SC3.2 in Tables 2and 3.

TABLE 4 Relative GLogCh-ID Priority RB-Type Routing 65 3 High Prio SC3.1Signaling 66 3 High Prio SC3.1 Signaling 67 6 Low Prio SC3.1 Signaling68 8 Best Effort SC3.1 69 5 SIP Signaling SC3.1 70 4 VolP SC3.1 71 7Video Streaming SC3.1 101 2 High Prio Signaling 102 2 High PrioSignaling 103 5 Low Prio Signaling 104 2 High Prio Signaling 105 2 HighPrio Signaling 106 5 Low Prio Signaling

According to this invention, small cell base station SC3.1 receives datafrom the UE device (UE) via any of the radio bearers. Assuming user datapackets arriving from all data radio bearers, i.e. DRB1, DRB2, DRB3 andDRB4. Small cell base station SC3.1 receives the packets, decodes andde-multiplexes them and re-assembles segmented packets into originaluser data packets. In most cases, these are IP-packets from respectiveapplications. In other examples where packets are received fromsignaling radio bearers SRB0, SRB1 or SRB2, the packets may not beIP-packets but RRC messages from the RRC layer of the UE device UE. Now,SC3.1 determines for each user data packet based on the radio bearerfrom which the packet was received and based on the configuration by theDgNB a Global Logical Channel Identifier GLogCh-ID and appends it to thedata packet before forwarding the packet via the wireless backhaul tothe small cell base station SC2. That is, for packets received from theUE device UE on data radio bearer DRB1 a GLogCh-ID=68 is appended beforeforwarding the data via the wireless backhaul. For data radio bearersDRB2, DRB3 and DRB4, the GLogCh-IDs 69, 70 and 71 are appended,respectively. The appending may be done according to any suitableprotocol, e.g. any of the existing protocols in the 5G NR protocol stackor a new protocol as named example wise in FIG. 2 as Relay Protocol“RP”. The forwarding of the packets is done according to theconfiguration by the DgNB, i.e. according to the configuration data ofTable 2. The table provides for each of the UE device's radio bearers arelative priority with which the data is treated with respect to theorder of transmitted packets that are multiplexed onto the sameresources. Higher priority, i.e. smaller integer values of the relativepriority parameter, lead to a prioritized transmission while lowerpriority packets are only transmitted if no higher priority packets arepending transmission. Table 2 also provides for each of the UE device'sradio bearers a RB-Type information, which may also be called quality ofservice, QoS, which indicates the nature of the services the dataoriginates from. The RB-Type may be used by the small cell base stationto select one of the five data radio bearers DRB4 to DRB8 of the smallcell base station for forwarding of the data packet. The same principleis applied to data packets received in small cell base station SC3.1from the UE device UE over one of the signaling radio bearers SRB0, SRB1or SRB2 with respective higher priority, different QoS or RB-Type andGLogCh-ID 65, 66 or 67, respectively.

The small cell base station SC2 receiving a data packet from small cellbase station SC3.1 via any of the data radio bearers DRB1, DRB2, DRB3,DRB4 or DRB5 on the wireless backhaul link of SC3.1 will decode andde-multiplex the packets, re-assemble segmented packets and determinethe appended GLogCh-ID. It will look up the GLogCh-ID according to theconfiguration by the DgNB, e.g. the look up of an example packet fromthe UE device with LogCh-ID=68 leads to a forwarding by SC2 according toa quality of service “Best effort” and relative priority 8. The smallcell base station SC2 does not have any information about the UE deviceUE nor does it need to associate the GLogCh-ID=68 to a specific device.However, it receives enough information to determine a forwardingtreatment of the packet with respect to QoS and priority and byforwarding also the GLogCh-ID together with the received data packet, itprovides enough information for further small cells to determine aforwarding treatment and to the DgNB to associate the packet to aspecific UE device. Assuming small cell base station SC2 has setup abearer to the DgNB that is suitable to transport best effort data, it isused, and data is multiplexed onto available resources according topriority 8.

The DgNB has the information about the mapping of GLogCh-IDs allocatedin the subnetwork controlled by the DgNB to UE devices and respectiveradio bearers of the UE devices so that after successful reception of apacket the DgNB can determine based on the GLogCh-ID the correct PDCPand/or RRC entity to which the packet is addressed.

The above describes the UL data transfer from UE device to the DgNB viathe multi-hop subnetwork. For the DL the same principles can apply, i.e.a GLogCh-ID is appended by the DgNB to any data packets transmitted to asmall cell base station, e.g. SC2. The small cell base station SC2determines the GLogCh-ID, looks up the respective QoS and priority andforwards the data packets with the LogCh-ID. In order for the small cellbase station to determine the route, i.e. to which of the served devicesa data packet should be routed, the DgNB has configured a routinginformation into small cells for devices they do not serve with anaccess link. In the given example, this is small cell base station SC2and the routing configuration is depicted example wise in the “routing”column of Table 4.

In that table, all radio bearers to/from the UE device are routed viasmall cell base station SC3.1. The routing information may be providedin the form of a next hop address or a next hop device name, the latterbeing shown in Table 4. The routing information may alternatively beprovided with an index of a next hop, the index pointing to apre-configured table.

Table 4 does not comprise routing information for radio bearers of smallcell base station SC3.1 and SC3.2 as both small cell base stations areserved with an access link by SC2 and thus the GLogCh-ID of any packetmaps to the respective radio bearer of the access link and thus to thefinal device.

Looking now at FIG. 4 , the description above mainly explained firstlythe pre-assumption of an established RRC connection of every UE deviceand small cell base station with the DgNB, which is shown in the figurein the top box. Secondly, the above describes the data transfer betweena UE or other devices to and from the DgNB, which is shown simplified inthe figure with the top-most double arrows.

According to the current invention, the DgNB configures the UE device UEwith candidate cell information comprising in this embodimentinformation about a cell spanned by small cell base station SC3.2. Theinformation may comprise resource information, e.g. a frequency band ora mid-frequency of the cell bandwidth of the candidate cell. Theinformation may also comprise a cell identity, e.g. a physical cellidentity encoded in the synchronization signals broadcasted in the cellto allow a cell identification on the base of the synchronizationsignals. The information may further comprise a UE device identity to beused by the UE device when accessing the candidate cell. In thisembodiment it is assumed that the UE device identity, e.g. the C-RNTI,is not changed when switching between cells autonomously. For randomaccess or other data limited ways of accessing a candidate cell, the UEdevice and the candidate cell may be configured with a short UE deviceidentity in addition or instead of the C-RNTI.

In addition, the candidate small cell SC3.2 is configured so that it isable to serve the UE device after an autonomous cell switch of the UEdevice. For that purpose, SC3.2 is configured with the UE deviceidentity, in this embodiment the C-RNTI and/or a short UE deviceidentity, and further information needed to serve the UE. For example,UE radio capabilities related to the MAC and physical layer areconfigured.

In addition, the information according to Table 1 which is currentlypresent in the UE device and in the small cell base station SC3.1 forserving the UE device, is also configured into small cell base stationSC3.2. This information enables SC3.2 to multiplex DL data onto theappropriate radio bearers and forward UL data with appropriate QoS andpriority and appending the correct GLogCh-ID as explained further abovefor small cell base station SC3.2.

Now, the small cell base station SC3.2 broadcasts synchronization andreference signals as well as system information which is received by theUE device and a measurement of the candidate cell SC3.2 is derived thatis used by the UE device to decide on a potential cell switch. Theinformation broadcasted by SC3.2 is shown as a dashed line in the figurebecause this is just an example and any other kind of trigger for the UEdevice to decide on a cell switch may be used to implement thisinvention. The system information may comprise load information thathelps the UE device to determine whether the service that can beexpected from SC3.2 is better than the service of the currently servingSC3.1.

According to this embodiment the UE device determines to switch cellautonomously and request resources from the candidate small cell basestation SC3.2. This may be done by performing a random access to thecandidate small cell using the short UE device identity that wasconfigured. The UE device may request in a first random-access messageresources for a longer second message sent on the granted resources.Alternatively, if no random-access is required, e.g. for timing reasons,the UE may directly use a physical uplink control channel for requestingUL resources using the C-RNTI.

During that procedure, the DL data transfer via small cell base stationSC3.1 may continue. Depending on the UE device radio capabilities, theUE device may be able to successfully receive data from SC3.1 andacknowledging the reception in UL while starting the UL data transfer toSC3.2. This option is shown with dashed lines in FIG. 4 .

The candidate small cell SC3.2 may reply to the UL resource request witha UL resource grant which, when received by the UE device, may changethe candidate small cell SC3.2 into the new serving small cell. The UEdevice compiles first UL data packets, e.g. from user data packets or anUL RRC message, and transmits these to the small cell base stationSC3.2. The packets are received and the mapping of configured radiobearers onto the radio bearers of the wireless backhaul link is done asdescribed for the UL packet forwarding of small cell base station SC3.1including the appending of the GLogCh-ID in an appropriate communicationprotocol.

According to the present invention, as soon as UL data packets from theUE device are received in small cell base station SC2, recognized bytheir LogCh-ID, the duplication of DL data packets to the UE device ofthe same bearer, recognized by the same LogCh-ID, is started.Duplication in this sense means that these DL packets are transmitted bythe small cell base station along the old route, i.e. to small cell basestation SC3.1 in this embodiment, and in addition they are copied to thenew route from which the first UL packets have been received, i.e. smallcell base station SC3.2.

In case the GLogCh-ID is built so that it allows identification of allbearers belonging to a single UE device, the principle of temporarilycopying DL data packets in a small cell base station may be applied toall bearers of a UE once a first UL data packet has been received. Incase the GLogCh-ID does not allow distinction of UEs, the DL copying canonly be applied to bi-directional bearers for which UL packets have beenreceived. In that case it may be foreseen that the UE device transmitsdummy packets in UL for bearers that currently don't have UL data tosend to allow for a fast usage of the new route in DL for all bearers.These dummy packets could be of zero user data length, i.e. only containa small header, or they may otherwise be marked so that they areeliminated from the data flow within the radio access sub-network.

The reception of a first DL packet by the UE via the new small cell basestation SC3.2 or the first UL grant or successful reception of an ULpacket acknowledge by the new small cell base station may trigger the UEdevice to inform the DgNB about the successful execution of a cellswitch in an RRC message, e.g. “path switch Info”. The reception of thismessage in the DgNB may trigger the DgNB to inform all involved smallcells about the path switch, i.e. small cell base station SC2 isrequested to manifest the new route to the UE, small cell base stationSC3.2 is requested to function as serving small cell and SC3.1 isconfigured to delete the UE context or it is configured as a candidatesmall cell for a future cell switch back to the old cell.

In case the small cell base station SC2 copied the DL packets for only apart of the bearers of the UE device, the DgNB may trigger the routemanifestation now for all bearers of the UE device.

Now, DL data transfer for all bearers of the UE device takes the routeto the new small cell base station. A new configuration of the UEproviding new candidate small cells may be performed by the DgNBthereafter.

A variation of the previous is shown in FIG. 5 based on the samesub-network architecture of FIG. 3 . The pre-requisite of RRCconnections of the UE device and all small cell base stations with theDgNB and the configuration of small cell base stations SC3.1 and SC2with GLogCh-IDs and routing information is the same as in the previousembodiment.

In this embodiment, according to a new aspect of this invention, thesmall cell base station SC3.1 is configured to inform the DgNB if aconnection to a UE device is lost. The small cell SC3.1 informs the DgNBof a loss of connection to the UE by transmitting a UE device identityor it informs of a loss of connection to served bearers by transmittinga list of GLogCh-IDs to which connection has been lost. Either of theinformation can be transmitted in a kind of “bearer loss notification”to the DgNB.

In FIG. 5 , at a point in time, the UE device and the small cell basestation SC3.1 detect loss of connection, e.g. due to a radio linkfailure as a result of the UE leaving the cell or a shadowing of the UEantenna or alike. The UE device will start buffering the UL data rightaway, as no link for transmitting is available. This is not different tostate of the art UE device implementations. According to this invention,the small cell base station SC3.1 informs the DgNB about a loss ofconnection to the UE device and the DgNB will start buffering DL data.The DgNB may also start a timer which, when it expires, triggers animplicit release of the RRC connection to the UE device. In thisembodiment, it is assumed that the timer does not expire and the RRCconnection is maintained.

The UE device performs the autonomous cell switch to a candidate smallcell, in this embodiment SC3.2 and transmits in the UL, preferably as afirst UL packet, an RRC message informing the DgNB about the pathswitch. The RRC now re-configures the impacted small cells SC2, SC3.1and SC3.2 about the new path to and from the UE device and startstransmitting the buffered DL data before the regular DL data transfer ofnew data is continued. The UE may start UL data transfer right after isautonomously switched cell.

A further embodiment will now be described. This embodiment is anamendment of a part of the previous embodiments in an architectureaccording to FIG. 6 . In comparison to the architecture of FIG. 3 thedepicted sub-network has one layer of hierarchy more. This embodimentshould show a useful aspect of the present invention for biggersub-networks.

Assuming all five small cell base stations of the sub-network areconfigured to actually or potentially serve the UE device, an individualconfiguration of the small cell base station according to the previoustwo embodiments consumes significant radio resources on the wirelessaccess links. An alternative is shown in FIG. 7 . The DgNB broadcasts asmall cell reconfiguration message comprising the small cell routingpreparation information, i.e. the GLogCh-IDs and related QoS, priorityand routing information. Broadcast in this sense means a distribution toall directly connected small cell base stations of the sub-network withthe purpose to store and apply the configuration and in parallel forwardthe information by every small cell base station to the next small cellbase stations directly connected via an access link.

According to FIG. 7 , all small cell base stations receiving thereconfiguration message forward the message, verify its integrity, e.g.by verifying their integrity based on a certificate stored in each smallcell base station received from the network operator beforehand. Whenthe integrity is verified, the configuration is stored and applied.

This is an efficient distribution mechanism for the configuration of thesub-network that can be combined with the core steps of the presentinvention described in an exemplary manner for the first twoembodiments.

Any reconfiguration of a UE device or small cell base station of thesub-network that leads to an addition, a removal or a significantreconfiguration of a signaling or data bearer will then lead to abroadcast of a small cell reconfiguration message comprising updatedGLogCh-ID, priority, QoS and/or routing information, so that all smallcell base stations are prepared to serve UE devices after an autonomouscell switch. If the efficient broadcast mechanism of the thirdembodiment is not used, any such reconfiguration of a UE device or smallcell base station will lead to an individual reconfiguration of allimpacted small cell base stations.

A fourth embodiment is based on an architecture depicted in FIG. 8 whichis similar to the architecture of FIG. 3 except that small cell basestation SC3.2 is directly connected to the DgNB. SC3.2 may be optimizedfor low latency and limited bandwidth communication.

The UE device may have several applications running that have a QoS thatdoes not require low latency communication. In addition, the UE has oneapplication that sporadically generates data packets requiring a lowlatency transmission (ULL data) and that usually generate a limitedamount of DL traffic, e.g. a single acknowledgement on the networklayer.

FIG. 9 shows a message sequence according to this embodiment. The UEdevice is assumed to be connected to small cell base station SC3.1 andhave an RRC connection with the DgNB similar to the first embodiment TheUE device is configured with at least one candidate cell SC3.2, this isa candidate for transmission of ULL data. This cell is not consideredfor autonomous cell switching as in the other embodiments, but it isconsidered for autonomous selection for ULL data transmission. The smallcell base station SC3.2 is configured as a candidate cell, but theconfiguration may be limited to supporting the ULL data radio bearers,e.g. a single GLogCh-ID and no signaling radio bearers of the UE device.

At a point, ULL data is generated by the respective application, the UEdevice selects the candidate cell SC3.2 for transmission and requests ULtransmission resources while UL and DL transmission via the small cellbase station SC3.1 continues for other applications, i.e. other radiobearers, or for RRC signaling. After a grant the UE device transmits theULL data in UL which is routed according to the small cell configurationto the DgNB. The resulting DL data is routed the same routed andreceived from SC3.2 in the UE device. Optionally, the UE device mayinform the DgNB about the data transmission on the newly selected smallcell base station SC3.2 and the DgNB may re-configure the small cellbase station and confirm the new path. This is described here asoptional and shown in FIG. 9 with dashed lines as for a single datatransmission, any involvement of the DgNB beyond the data routing may beomitted.

Particular aspects of the invention may be summarized as follows.

A base station controlling a radio access subnetwork, the radio accesssubnetwork comprising at least one UE device and multiple cascaded smallcell base stations, the at least one UE device and multiple cascadedsmall cell base stations having an RRC connection to the base station,

-   -   the multiple cascaded small cell base stations further        comprising multiple small cell base stations each having a        wireless backhaul link to another small cell base station,    -   at least one small cell base station having a wireless backhaul        link to the base station    -   multiple small cell base stations each having a wireless access        link to other small cell base stations,    -   at least one small cell base station having a wireless access        link to the at least one UE device,        the base station    -   configuring the UE device with candidate small cell information,        the candidate small cell information comprising identification        information of at least one candidate small cell spanned by one        of the multiple cascaded small cell base stations for autonomous        cell switching and at least one condition for the execution of        the autonomous cell switching, and    -   configuring at least one small cell base station as a candidate        small cell base station for having a wireless access link to the        at least one UE device after an autonomous switch by the UE        device, the configuring as a candidate small cell base station        comprises configuration of        -   a UE device identification used by the UE device when            accessing the candidate small cell,        -   one or more bearer identifiers identifying one or more            bearers of the UE device, and        -   forwarding treatment information for each of the one or more            bearer identifiers, the forwarding treatment information            comprising at least one of quality of service parameters,            priority information and routing information for forwarding            data packets from or to the UE device received by the            candidate small cell base station, and    -   receiving information about a cell switch executed by the UE        device autonomously, (the cell switch execution not being        triggered by the station).

The base station above capable of configuring, after receiving theinformation about a cell switch executed by the UE device autonomously,the UE device with updated candidate small cell information. Also,confirming, after receiving the information about a cell switch executedby the UE device autonomously, a path switch in small cell base stationsinvolved in routing data from or to the UE device.

A base station controlling a radio access subnetwork, the radio accesssubnetwork comprising at least one UE device and multiple cascaded smallcell base stations, the at least one UE device and multiple cascadedsmall cell base stations having an RRC connection to the base station,

-   -   the multiple cascaded small cell base stations further        comprising        -   multiple small cell base stations having a wireless backhaul            link to another small cell base station,        -   at least one small cell base station having a wireless            backhaul link to the base station        -   multiple small cell base stations having a wireless access            link to other small cell base stations, and        -   at least one small cell base station having a wireless            access link to the at least one UE device,    -   the base station        -   configuring the UE device with candidate small cell            information, the candidate small cell information comprising            identification information of at least one candidate small            cell spanned by one of the multiple cascaded small cell base            stations for autonomous cell switching and at least one            condition for the execution of the autonomous cell            switching, and        -   configuring at least one small cell base station for routing            data of one of the at least one UE devices, the configuring            comprises configuration of            -   one or more bearer identifiers identifying one or more                bearers of the UE device, and            -   forwarding treatment information for each of the one or                more bearer identifiers, the forwarding treatment                information comprising at least one of quality of                service parameters and priority information,            -   routing information for routing downlink data packets                received on the wireless backhaul link to the UE device,                the routing information comprising at least one first                path for routing downlink data packets to the UE device,                and at least one alternative path for routing downlink                data packets to the UE device after an autonomous cell                switch by the UE device, and        -   in response to receiving information via one of the at least            one alternative paths about a cell switch executed by the UE            device autonomously, confirming a path switch to the small            cell base station.

The base station as above, wherein the confirming a path switch to thesmall cell base station comprises requesting to terminate duplication ofdata packets to the first path.

The base station as above, wherein configuring at least one small cellbase station for routing data of one of the at least one UE devicescomprises providing identical configuration information to all smallcell base stations having an access link to the base station forconfiguration of the small cell base stations and for forwarding theconfiguration information by the small cell base stations to furthersmall cell base stations, the configuration information being integrityprotected so that small cell base stations can verify the integrity ofthe configuration data.

A UE device for executing autonomous cell switching, the UE device

-   -   having a wireless access link to a first small cell base        station,    -   having an RRC Connection to a macro base station controlling the        first small cell base station and the UE device,    -   receiving from the macro base station a UE device identification        information and candidate small cell information, the candidate        small cell information comprising        -   identification information of at least one candidate small            cell, and        -   at least one condition for the execution of an autonomous            cell switching,            wherein the UE device, based on measurements of signals            received from a candidate small cell and the at least one            condition for the execution of the autonomous cell            switching, determines autonomously to execute a cell switch            to the candidate small cell and requests uplink resources            for data transmission from the candidate small cell using            the UE device identification information.

The UE device as above which autonomously determines to execute a cellswitch without receiving a message triggering the cell switch to thecandidate small cell and without informing the first small cell basestation about the cell switch execution. Also, a UE device as abovewhich executes the cell switch while data transfer to and/or from thefirst small cell base station is ongoing.

The UE device may be arranged such that after successful execution ofthe cell switch it informs the base station in an RRC message sent viathe switched-to small cell about the execution of the cell switch,wherein the execution of the cell switch is deemed successful afterreceiving from the switched-to small cell one of an uplink resourcegrant and a downlink data packet.

After receiving from the base station neighbour cell measurementinformation, the neighbour cell measurement information comprisingidentification information of at least one cell not controlled by thebase station, and

-   -   while (or in parallel to, but actually never really        simultaneously) measuring received signals of candidate small        cells from the identification information of at least one        candidate small cell to determine whether to execute an        autonomous cell switch, the UE device may perform neighbour cell        measurements according to the neighbour cell measurement        information.

The UE device may report neighbour cell measurements to the macro basestation according to the neighbour cell measurement informationindependent of the autonomous cell switch.

A small cell base station controlled by a base station having a wirelessbackhaul link to another small cell base station controlled by the basestation, the small cell base station

-   -   receiving from the macro base station UE device information, the        UE device information comprising        -   a UE device identifier identifying a UE device not currently            served by the small cell base station,        -   one or more radio bearer identifiers uniquely identifying            (within a subnetwork controlled by the base station) one or            more radio bearers of the identified UE device, and        -   forwarding treatment information associated with the one or            more radio bearer identifiers, the forwarding treatment            information comprising at least one of quality of service            information, priority information and routing information,    -   receiving from the UE device a request for uplink resources, the        request comprising a UE device identifier,    -   identifying the UE device based on the respective UE device        identifiers received from the UE device and from the macro base        station,    -   granting uplink resources to the identified UE device without        further communication relating to the UE device with the macro        base station, and    -   receiving an uplink data packet on a radio bearer from the UE        device, determining the radio bearer identifier uniquely        identifying the radio bearer of the UE device and forwarding the        data packet together with the determined radio bearer identifier        to the another small cell base station via the wireless backhaul        link according to the forwarding treatment information.

A small cell base station controlled by a base station having a wirelessbackhaul link (to another base station) and having wireless access linksto at least two further small cell base stations controlled by the basestation, the small cell base station receiving from the base station

-   -   one or more bearer identifiers each identifying one or more        bearers of a specific UE device, and    -   forwarding treatment information associated with the one or more        identified bearers, the forwarding treatment information        comprising at least one of quality of service information and        priority information,    -   routing information for routing downlink data packets received        on the wireless backhaul link to the specific UE device, the        routing information comprising at least a first and a second        path for routing downlink data packets to the specific UE        device,    -   the small cell base station, while transmitting all downlink        data packets identified by a bearer identifier to be routed to        the specific UE device along the first path contained in the        routing information, in response to receiving at least one        uplink data packet from the specific UE device on (an access        link of) the second path contained in the routing information,        starting to transmit all downlink data packets identified by a        bearer identifier to be routed to the specific UE device along        the second path.

The small cell base station may be arranged such that starting totransmit all downlink data packets identified by a bearer identifier tobe routed to the specific UE device along the second path comprisestransmitting a copy of all downlink data packets identified by a beareridentifier to be routed to the specific UE device in addition along thefirst path contained in the routing information, and

-   -   the small cell base station stopping to transmit a copy of all        downlink data packets identified by a bearer identifier to be        routed to the specific UE device along the first path contained        in the routing information after receiving a confirmation        message from the macro base station via the wireless backhaul        link, the confirmation message confirming the path switch.

The invention claimed is:
 1. A mobile communication system sub-networkcomprising a macrocell base station and a plurality of small cell basestations, the plurality of small cell base stations being in wirelesscommunication with the macrocell base station, wherein each small cellbase station is either in direct connection with the macrocell basestation or is in connection with the macrocell base station via one ormore other small cell base stations, wherein the macrocell base stationis arranged to configure a user equipment (UE) device having a radioresource control, RRC, connection to the macrocell base station toperform autonomous switching between small cell base stations usingcandidate small cell base station configuration information provided bythe macrocell base station to the UE device, and wherein the macrocellbase station is arranged to configure the small cell base stations withsmall cell base station configuration information comprising a UE deviceidentifier identifying a UE device configured by the macrocell basestation with the candidate small cell base station configurationinformation and comprising one or more sub-network unique identifiersuniquely identifying one or more radio bearers of the UE device, thesmall cell base station configuration enabling the small cell basestations to, upon identifying the UE device based on receiving the UEdevice identifier, receive data from the UE device on a radio bearer ofthe one or more radio bearers of the UE device, to determine asub-network unique identifier uniquely identifying the radio bearer, andto forward the data together with the determined sub-network uniqueidentifier to either the macrocell base station or another small cellbase station.
 2. The mobile communication system sub-network of claim 1,wherein the sub-network unique identifier uniquely identifies the radiobearer and the UE device within the mobile communication sub-network. 3.The sub-network according to claim 2, wherein the small cell basestation configuration information comprises information selected from alist comprising medium access control, MAC, layer configurationelements, physical layer configuration elements, a global identifier tobe transmitted to the macrocell base station together with data receivedfrom the UE device and routing information for transport of uplinkand/or downlink information from or to the UE device, the sub-networkunique identifier uniquely identifying a radio bearer and the UE devicewithin the mobile communication sub-network.
 4. The sub-networkaccording to claim 2, wherein the small cell base stations have a cellcoverage less than a cell coverage of the macrocell base station.
 5. Thesub-network according to claim 4, wherein each small cell base stationis arranged to multiplex data received from different radio bearers ontoa single bearer for transmission towards the macrocell base station, themultiplexing being dependent on a quality of service setting of thereceived data radio bearer, and wherein an indication of the originatingradio bearer is added to transmitted data packets.
 6. The sub-networkaccording to claim 1, wherein the candidate small cell base stationinformation comprises information selected from a list comprising smallcell base station identities, small cell base station frequencyresources, small cell base station radio parameters, small cell basestation mode of access and small cell base station switching criteria.7. The sub-network according to claim 6, wherein the small cell basestations have a cell coverage less than a cell coverage of the macrocellbase station.
 8. The sub-network according to claim 7, wherein eachsmall cell base station is arranged to multiplex data received fromdifferent radio bearers onto a single bearer for transmission towardsthe macrocell base station, the multiplexing being dependent on aquality of service setting of the received data radio bearer, andwherein an indication of the originating radio bearer is added totransmitted data packets.
 9. The sub-network according to claim 1,wherein the small cell base station configuration information comprisesinformation selected from a list comprising medium access control, MAC,layer configuration elements, physical layer configuration elements, aglobal identifier to be transmitted to the macrocell base stationtogether with data received from the UE device and routing informationfor transport of uplink and/or downlink information from or to the UEdevice, the sub-network unique identifier uniquely identifying a radiobearer and the UE device within the mobile communication sub-network.10. The sub-network according to claim 9, wherein the small cell basestations have a cell coverage less than a cell coverage of the macrocellbase station.
 11. The sub-network according to claim 1, wherein thesmall cell base stations have a cell coverage less than a cell coverageof the macrocell base station.
 12. The sub-network according to claim11, wherein each small cell base station is arranged to multiplex datareceived from different radio bearers onto a single bearer fortransmission towards the macrocell base station, the multiplexing beingdependent on a quality of service setting of the received data radiobearer, and wherein an indication of the originating radio bearer isadded to transmitted data packets.
 13. The sub-network according toclaim 1, wherein the macrocell base station is arranged to provide anidentifier of the UE device to those of the small cell base stationswhich may be involved in routing data packets from the UE device to themacrocell base station, the identifier being used by the UE device torequest radio resources from the small cell base stations.
 14. Thesub-network according to claim 1, wherein the macrocell base station isarranged to provide the small cell base stations with informationconcerning all sub-network served radio bearers and devices togetherwith their radio priorities and quality of service settings.
 15. Thesub-network according to claim 1, wherein the small cell base stationconfiguration information comprises routing information for routingdownlink packets received on a wireless backhaul link to the UE device,the routing information comprising at least one first path for routingdownlink data packets to the UE device and at least one alternative pathfor routing downlink packets to the UE device after an autonomous cellswitch by the UE device.
 16. The sub-network according to claim 15,wherein the macrocell base station is arranged to confirm a path switchfrom a first small cell base station to a second small cell base stationin response to receiving information via one of the at least twoalternative paths about a cell switch performed by the UE device. 17.The sub-network according to claim 15, wherein the small cell basestation configuration information provides identical configurationinformation to all small cell base stations having a direct connectionto the macrocell base station for configuration of the small cell basestations and for forwarding the configuration information by the smallcell base stations to further small cell base stations, theconfiguration information being integrity protected so that small cellbase stations can verify the integrity of the configuration data.
 18. Auser equipment (UE) device arranged to be able of autonomous cellswitching in a mobile communications system sub-network comprising amacrocell base station and a plurality of small cell base stationsproviding cells between which the UE device can switch, wherein the UEdevice is arranged to receive from the macrocell base station with whichit has a radio resource control connection UE device identificationinformation and candidate cell information, the candidate cellinformation comprising identification information and at least onecondition for initiating autonomous cell switching between a first and asecond small cell base station, the UE device identification informationcorresponding to UE device identification information received from themacrocell base station by the first and second small cell base station,wherein the UE device is arranged to: request uplink resources for datatransmission from a candidate cell using the UE device identificationinformation, and transmit uplink data on a radio bearer using uplinkresources received from the candidate cell; trigger the candidate cellby way of transmitting the uplink data to determine, based on receivingthe UE device identification information, a sub-network uniqueidentifier uniquely identifying the radio bearer and the UE device andforwarding the data packet together with the determined sub-networkunique identifier to another small cell base station via a wirelessbackhaul link.
 19. A small cell base station controllable by a macrocellbase station, the small cell base station being arranged to receive fromthe macrocell base station user equipment (UE) device information, theUE device information comprising a UE device identifier identifying a UEdevice not currently served by the small cell base station, one or moresub-network unique identifiers uniquely identifying one or more radiobearers of the identified UE device, and forwarding treatmentinformation associated with the one or more sub-network uniqueidentifiers, the forwarding treatment information comprising at leastone of quality of service information, priority information and routinginformation, the small cell base station being further arranged to:receive from the UE device a request for uplink resources, the requestcomprising a UE device identifier, identify the UE device based on theUE device identifier received from the UE device and from the macrocellbase station, grant uplink resources to the identified UE deviceautonomously, and receive an uplink data packet on a radio bearer fromthe UE device, determining a sub-network unique identifier of the one ormore sub-network unique identifiers uniquely identifying the radiobearer of the UE device and forwarding the data packet together with thedetermined sub-network unique identifier to another small cell basestation via a wireless backhaul link according to the forwardingtreatment information.
 20. A method of operating a mobile communicationsub-network comprising a macrocell base station and a plurality of smallcell base stations connected to the macrocell base station by means of awireless connection, wherein the small cell base stations are either indirect connection with the macrocell base station or are in connectionwith the macrocell base station via one or more other small cell basestations, the method comprising: enabling by the macrocell base stationa UE device in connection with the macrocell base station via a firstone of the small cell base stations to autonomously transfer theconnection such that it passes via a second one of the small cell basestations by determining a locally unique identifier, distributing thelocally unique identifier to the plurality of small cell base stationsvia a wireless backhaul link, the macrocell base station receiving fromthe second one of the small cell base stations data originating from aradio bearer of the UE device, the data received together with thelocally unique identifier, and identifying from the locally uniqueidentifier the UE device and the radio bearer, the macrocell basestation further identifying a data flow of the UE device on the wirelessbackhaul link on a radio bearer upon identifying the UE device based onthe local unique identifier, the locally unique identifier being uniquefor the UE device to the macrocell base station and the plurality ofsmall cell base stations, and identifying, a radio bearer to originatefrom the UE device on the wireless backhaul link.